In many applications, for example throughout instrumentation, metrology and like precision disciplines, one element of an instrument or tool must be supported in precise relation to another element, or to a workpiece. For example, in microscopy, particularly as used for precision measurement of features of an object, the optical components of the microscope must be mounted in a stable and precisely defined relationship to the stage on which the object being examined is mounted. The invention relates to a structure for thus rigidly supporting one component of an instrument or tool to another component or to a workpiece. It would further be desirable if such a structure could be manufactured readily, avoiding casting and other complex manufacturing techniques, and if the structure consumed a minimal amount of space, so as to provide access to the equipment supported. Further advantages to be provided by such a structure would include ease of adjustability, ease of assembly and simplicity of design.
Conventional optical microscopes as used in inspection processes as described generally above typically comprise a heavy cast iron "C"-shaped structure, the microscope stage being mounted to the lower portion of the "C"-shaped structure, and the optical components of the microscope being mounted to the upper portion of the "C". Such heavy cast iron structures are very expensive to fabricate, and as increasing the mass of the structure is the only effective way of increasing its rigidity, increase substantially in weight and cost for any improvement in rigidity. Increasing the distance the stage and microscope are cantilevered out from the backbone of the "C" to improve access renders the overall structure more susceptible to vibration, requiring more material to provide adequate rigidity.
The prior art shows pin-connected truss or strut structures used to support one portion of a machine element or instrument with respect to a base. For example, see Kail U.S. Pat. No. 3,577,659 showing a three degree-of-freedom joint for attaching the upper end of linear actuators to a motion platform of a six degree-of-freedom motion system. More particularly, the Kail system provides a support structure for an aircraft cockpit simulator; the cockpit simulator is supported on six telescoping members, each pivotably joined to the support structure of the cockpit at one end and to support structure fixed with respect to the building floor at the opposite end. Each end of the Kail linear actuators is connected to its respective support structure by a ball joint such that the angles made by the actuators with respect to one another and the support structure can vary as the lengths of the actuators are varied. By controllably varying the length of the linear actuators, the cockpit simulator is provided with six degrees of freedom, allowing the simulation of a variety of rolling, pitching, and yawing motions as might be encountered in flight.
The Kail linear actuators are connected to the floor of the building and the cockpit simulator such that each pair of actuators and the support structure essentially forms a triangle; the resulting structure is relatively rigid. However, because the points at which the center lines of the actuators intersect the support structure are spaced from one another, a pivoted link is effectively introduced between two sides of each triangle. The rigidity of the structure is therefore significantly reduced. Moreover, bending loads are experienced by the actuators, rendering them more susceptible to vibration than would otherwise be the case. Furthermore, the Kail structure is relatively complex and thus costly to manufacture.
Davister U.S. Pat. No. 5,088,852 shows a pinned connector structure for connecting struts of a geodesic dome or the like at nodes. Depending on the precise alignment used, the struts of the Davister assembly could intersect at the center lines of the nodes. However, the structure shown in Davister is very complicated to fabricate, and does not provide a satisfactorily simple method for fixing the nodes with respect to a structure to be supported, a ground plane, or the like.
U.S. Pat. No. 4,934,840 to Paret shows a spherical bearing assembly wherein a number of ball bearings supporting a larger spherical bearing are contained within a sealed race.
Walters U.S. Pat. No. 4,928,546 shows a robotic device wherein a plurality of members approximating the fingers of one's hand are joined to sections of a sphere for allowing independent motion in a plane.
Halford et al U.S. Pat. No. 2,260,283 is generally of interest in showing a split ball and socket joint. U.S. Pat. No. 1,059,313 to Perkins shows a step bearing for machinery, wherein a ball is supported within a recess and used to support another member.